Steam circuit process device and method for controlling the same

ABSTRACT

The invention relates to a steam circuit process device, comprising a reservoir for a liquid working medium; an evaporator in which the working medium is evaporated by heat supply, the vaporous working medium being fed to an expander for expansion and for carrying out mechanical work and being subsequently liquefied in a capacitor which communicates with the reservoir; a working medium pump for supplying working medium from the reservoir to the evaporator. The invention is characterized in that liquid working medium is supplied in the direction of flow of the working medium upstream or in the region of the capacitor to the working medium exiting the expander.

The invention relates to a steam circuit process device and a method for controlling the same, the steam circuit process device particularly forming a part of a vehicle drive or an auxiliary transmission drive in a vehicle.

Steam circuit processes, for example, a Clausius-Rankine process, for generating mechanical power from a heat flow are known and may be driven, for example, by a separate burner unit in a power-heat coupling apparatus. For vehicles, steam circuit process devices are preferably used to exploit waste heat of an internal combustion engine, the coolant water flow of the internal combustion engine or preferably its exhaust gas flow being used as the heat sources, depending on the selection of the working medium and the temperature control of the steam circuit process.

CH 171813 describes a steam power plant having a steam circuit, in which the following components are situated one behind another viewed in the flow direction of the working medium: a feed pump, a vaporizer, a superheater, a steam turbine, a condenser, and a working medium container. A shutoff valve is situated in the flow direction before the steam turbine, using which the inflow of vaporized working medium to the steam turbine can be completely interrupted. A first bypass for branching off a partial flow of liquid working medium is provided downstream from the feed pump. Furthermore, a second bypass is provided, using which the vaporized working medium can be conducted past the steam turbine. Both bypasses are connectable to one another to conduct flow via corresponding control valves. The second bypass is always opened when the shutoff valve in the supply line to the steam turbine is closed and the steam turbine is to be stopped, or if pressure spikes in the steam circuit occur as a result of the closing of the shutoff valve. Since the vaporized working medium would rest in the supply line in case of closing of the shutoff valve, the superheater would be destroyed because of the continually rising introduction of heat—since the heat energy for superheating the steam is not transferred to the flowing working medium and dissipated thereby. For this reason, upon closing of the shutoff valve, the control valves in the first and second bypasses are switched in such a manner that the vaporized working medium remains in movement (flows) and is conducted around the steam turbine. Simultaneously, in this case, liquid working medium is supplied from the first bypass downstream from the feed pump to the vaporized working medium, which is conducted past the steam turbine, for cooling in the connection line of both bypasses by opening corresponding control valves. The vaporized working medium which is conducted past collapses in the connection line in this case and is subsequently supplied via the second bypass to the condenser for further withdrawal of heat. The two bypasses therefore only represent a safety apparatus to prevent the destruction of the superheater and are further used to reduce pressure spikes in the circuit as a result of the closing of the valve in the fresh steam supply line to the expander. Power regulation of the expander is expressly not provided by this configuration.

For power control of steam circuit processes, a regulation of the volume flow of the working medium to the vaporizer is proposed by DE 102 29 250 A1. This presumes a working medium pump having variable delivery volume, in order to set a predefined volume flow value and/or pressure target value for the working medium in the supply line to the vaporizer. To implement this specification, a variable-speed drive can be assigned to the working medium pump, which makes an electric motor necessary for an electrically operated pump, but is disadvantageous for a vehicle drive because of the installation space required. Furthermore, it represents an additional electrical consumer. If the steam circuit process device is part of a vehicle drive having an internal combustion engine, alternatively, the working medium pump can be driven at variable speed by the internal combustion engine using a control clutch. However, this solution also has a complex design, is unfavorable with respect to the efficiency, and requires installation space for the additional control clutch.

Further controllers for the volume flow of the working medium in the supply line to the vaporizer are known from U.S. Pat. No. 4,573,323 and U.S. Pat. No. 4,020,637. A configuration of multiple pumps is disclosed in the first-mentioned publication, which take working medium from a reservoir or from an intermediate container, which is situated between a vaporizer and a superheater for the vapor phase of the working medium. One of these pumps is implemented as a controllable injector pump, which is mounted upstream from a pump driven at constant speed, whose delivery volume is a function of the intake-side to output-side pressure differential. Depending on the setting of the injector pump, working medium is either supplied from the intermediate container or the reservoir to the subsequent pump. It is not possible using this device, which is provided in particular for starting operation, to precisely adapt the volume flow of the working medium to the vaporizer in the meaning of a power regulation for the steam circuit process.

A steam circuit process device which is driven by a burner unit is known from above-mentioned U.S. Pat. No. 4,020,637. A part of the mechanical power generated at the expander is used to drive pumps for the working medium to the vaporizer and for the fuel supply to the burner unit. Through these measures, equilibrium exists in normal operation between the power delivery at the expander and the steam supply required for this purpose, which is in turn a function of the pressure in the working medium line and the burner temperature. If a disturbance of this equilibrium occurs, valves in bypass lines at the pumps are opened, which allow a recirculation of the working medium and/or the fuel to the pump intake side. The valves in the bypass lines function as directional control valves, i.e., as switches which may assume an on state and an off state. Furthermore, throttle points are provided in the bypass lines, in order to maintain the pressure gradient at the pump. Because of the design of the disclosed bypass lines, in case of opening of the bypass line, only a pressure spike is dissipated, so that the disclosed device does not allow regulation of the volume flow and/or the pressure of the working medium in the supply line to the vaporizer along a target curve, instead the above-described measures are only taken in case of overpressure. This is correspondingly true for the pump apparatus in the supply line to the burner.

Published application DE 195 24 171 A1 describes a low-temperature motor (low-temperature engine) for driving work machines using a gas as the working medium. Liquid gas is conveyed using a pump and supplied to a vaporizer. The vaporized gas performs work in a expansion machine and is subsequently cooled and liquefied in a relaxation element (condenser). The liquefied working medium is then supplied to a liquid collector (tank) and conveyed therefrom back via the pump. Furthermore, a bypass is provided, which branches off a part of the liquid working medium after the pump viewed in the flow direction of the working medium, and supplies it to the already relaxed, cooled, and therefore liquid working medium, which flows out of the condenser. A part of the working medium flowing out of the pump is therefore supplied directly to the liquid collector.

Alternatively, the working medium pump can be driven in a rotationally-fixed manner by the internal combustion engine. In such a drive, the working medium pump revolves as a function of the internal combustion engine speed, so that the delivered working medium volume flow is proportional to the speed of the internal combustion engine. In order to obtain a sufficiently high working medium volume flow to feed the vaporizer or the expander even at low to moderate engine speeds, larger-dimensioned pumps are correspondingly used. However, this also means that because of the rotationally-fixed coupling, a correspondingly higher working medium volume flow to the vaporizer is also generated at maximum speeds of the engine. The working medium volume flow conveyed by the working medium pump is therefore significantly greater than the required volume flow for the vaporizer or the expander.

Since the delivery volume flow is therefore always proportional to the engine speed and not to the occurring quantity of heat, optimal control of the steam parameters is not possible using this system. The quantity of heat to be dissipated by the condenser increases in relation to the useful power of the steam process due to the non-optimal process control. This is particularly disadvantageous if the steam circuit device is used in a motor vehicle, since the installation space available therein is limited and larger and heavier components result in higher fuel consumption.

The invention is based on the object of specifying a steam circuit process device and a method for controlling the same, which allow the condenser to be implemented as smaller and lighter than heretofore, in particular for applications in a motor vehicle or the drivetrain thereof. Preferably, a separate, variable-speed adjustable drive machine for the working medium pump is to be able to be dispensed with simultaneously and nonetheless the delivery volume of the working medium supplied to the vaporizer or expander is to be made variable for the purpose of power adaptation, or the pressure of the working medium in the supply line to the vaporizer is to be able to be adjusted in accordance with a target specification. A solution which is simple to design and manufacture is sought, which occupies a small installation space and additionally operates energy-efficiently.

The object according to the invention is achieved by a steam circuit process device and a method according to the independent claims. The dependent claims represent preferred embodiments of the invention.

The inventors have recognized that by branching off at least a part of the working medium volume flow upstream from the working medium pump and supplying the branched-off part to working medium leaving the expander downstream, the heat dissipation surface can be reduced and the condenser can be implemented having a smaller construction.

A steam circuit process device according to the invention comprises a reservoir for a liquid working medium and a vaporizer, in which the working medium is vaporized by heat supply, the vaporized working medium being supplied to an expander for expansion and performance of mechanical work and subsequently being liquefied in a condenser, which is connected to the reservoir. According to the invention, a working medium pump is provided for the supply of working medium from the reservoir to the vaporizer. Liquid working medium is supplied to the working medium exiting from the expander before or in the area of the condenser in the working medium flow direction.

Although the invention can be used particularly advantageously in motor vehicles, in particular rail vehicles, trucks, or passenger automobiles, it is also conceivable to use the steam circuit process device according to the invention or the control method according to the invention in other mobile apparatuses or stationary plants, in particular for exhaust gas energy reclamation in industrial plants. For example, the expander could be used to drive aggregates.

A bypass line is particularly advantageously provided for the supply of the liquid working medium, which produces a connection between an output side of the working medium pump and an intake side of the condenser. The bypass line can open directly into the pressure chamber of the working medium pump, for example, i.e., it can be situated inside the working medium pump or in a connection line to the vaporizer. The other end of the bypass line can also open directly into the condenser or into a line before the condenser in the working medium flow direction.

A further preferred embodiment provides that the end of the bypass line opens into a line between expander and condenser. Such a mouth can be implemented, for example, as a T-shaped connection pipe. However, other shapes are also conceivable.

Furthermore, an embodiment is preferred in which one end of the bypass line opens directly into the expander. The mouth can be provided in the outlet area, for example, i.e., downstream from the expansion chamber of the expander, so that the supply of liquid working medium which is conducted past the vaporizer occurs in the expander housing.

According to the above embodiments, the working medium which is supplied via the bypass line to the exit of the expander or the entry of the condenser is essentially provided in a (single) phase, namely the liquid phase. A single phase means that it is assumed that the state variables of the working medium cannot suddenly change, as is the case with cavities, for example. The mixing of the liquid phase of the working medium branched off via the bypass line with the vaporized phase of the exhaust steam of the expander first occurs in the line which conducts the exhaust steam of the expander or in the condenser.

The supply of liquid working medium branched off from the vaporizer to the working medium leaving the expander, which is typically completely vaporized, has the advantage that the steam is condensed or at least partially liquefied. Due to the collapse of the steam at the point of the supply of the liquid working medium, improved heat transfer and reduced volume of the working medium flowing from the expander into the condenser results, so that the heat transfer surface for dissipating the waste heat in the condenser can be implemented as smaller. Therefore, without supplying liquid working medium, at least the same quantity of heat as in typical larger condensers can be dissipated in the condenser in spite of smaller dimensioning.

The liquid surface of the liquid working medium is particularly advantageously enlarged in the area of the supply of the liquid working medium to working medium leaving the expander. An enlargement of the liquid surface can be performed by atomizing the branched-off liquid working medium, for example. For this purpose, for example, air can be supplied to the liquid working medium like an aerosol, so that a spray mist results. Such an atomization can be performed using a Venturi nozzle, for example. The liquid working medium can also be converted into a type of spray jet by a suitable nozzle solely using high pressure. The advantage of atomization is also that the working medium leaving the expander is mixed better with the supplied liquid working medium.

It is also conceivable to wet the pipe which guides the steam on the inner side using liquid working medium in the area of the combination of liquid and vaporized working medium.

A controllable valve can be provided in the bypass line, using which the pressure and/or volume flow of the working medium is (indirectly) regulated/controlled in the supply line to the vaporizer. The working medium quantity, i.e., the volume flow of the (liquid) working medium flowing into the vaporizer, is thus varied as a function of the temperature of the (vaporized) working medium leaving the vaporizer, in that a specific partial volume flow of liquid working medium is branched off using the bypass and conducted past the vaporizer, and supplied to the exit of the expander or the entry of the condenser. The branched-off volume flow can be adjusted, for example, by changing the opening cross-section of the controllable valve. In other words, the opening cross-section of the valve in the bypass line is varied as a function of the temperature of the working medium leaving the vaporizer to vaporize more or less liquid working medium. A supply flow control, i.e., an indirect adjustment of the pressure or volume flow of the vaporized working medium as a function of the liquid working medium, is thus achieved.

Corresponding sensors can be provided for this purpose, which record the (current) variables of the working medium (pressure, temperature, conveyed volume or mass flow or volume or mass flow branched off via the bypass line) of the working medium in the flow direction of the working medium before and/or after the vaporizer or before the expander, and transmit them for analysis via suitable lines to a corresponding regulating/control unit. Of course, these sensors may be introduced into the vaporizer, expander, or the corresponding connection lines to the vaporizer or expander themselves.

Using the regulating/control unit, the pressure and/or volume flow of the vaporized working medium generated in the vaporizer to the expander can be adjusted and/or varied as a function of the power demand at the expander. The volume flow and/or the pressure curve of the working medium in the supply line to the vaporizer (and therefore the volume flow and/or pressure curve of the vaporized working medium to the expander) can follow a predetermined target curve, which can be adjusted via the regulating/control unit. In this way, the waste heat utilization of the internal combustion engine can be used optimally for every operating point of the internal combustion engine. For example, in an operating point of the internal combustion engine in which a relatively large amount of heat occurs (high engine load, high engine speed), the liquid working medium volume flow which is branched off via the bypass can be supplied to the working medium (steam) exiting from the expander, whereby the steam collapses and liquefies.

Such a regulation/control can preferably always be performed, i.e., during the operation of the internal combustion engine, and particularly when a relatively large amount of waste heat occurs.

In a method according to the invention for controlling a steam circuit process device, the working medium volume flow delivered by the working medium pump varies independently of a target value for the pressure and/or the volume flow of the working medium to the vaporizer, and thus regulates and/or controls the working medium volume flow supplied to the vaporizer and/or expander in such a way that a part of the working medium volume flow from the working medium pump is supplied to the working medium exiting from the expander and therefore does not reach the vaporizer.

Preferably, the amount of the part of the working medium volume flow (partial volume flow) from the working medium pump to which the working medium exiting from the expander is supplied can be adjusted as a function of the temperature of the working medium exiting from the vaporizer. This means that the level of the partial volume flow can be adjusted using the opening cross-section of the controllable control valve and as a function of the temperature of the vaporized or overheated working medium after the vaporizer.

The invention will be explained for exemplary purposes hereafter on the basis of exemplary embodiments and the appended figures.

In the figures:

FIG. 1 shows, in schematically simplified form, a design of a steam circuit process device according to the invention.

FIG. 2 shows a further design of a steam circuit process device according to the invention.

FIG. 1 shows, in schematically simplified form, the basic components of a steam circuit process device. Liquid working medium is pumped using a working medium pump 1 to the vaporizer 2 from a reservoir 5. In the vaporizer 2, the vaporization of the working medium occurs, the thermal energy required from this purpose being supplied from a burner unit (not shown in detail). The steam circuit process device is particularly preferably part of a vehicle drive having an internal combustion engine, whose waste heat heats the working medium in the vaporizer 2. In particular the exhaust gases of an internal combustion engine come into consideration, the components required for this purpose not being shown in detail in FIG. 1 to simplify the illustration. The vaporizer 2 can be constructed as multistage, in particular, a superheating unit can be provided for the vapor phase.

The working medium is supplied in the vaporized state from the vaporizer 2 to the expander 3 via a line 8, in which it performs mechanical work while expanding. Following the expander 3, the working medium is liquefied in the condenser 4 and returned back into the reservoir 5.

The expander 3, which can generally also be referred to as a steam-driven engine, is implemented, for example, as a piston machine, steam turbine, or rotary machine.

An internal gear pump is used as the preferred working medium pump 1, whose speed is adjusted independently of the volume flow specification in the supply line to the vaporizer 2.

A bypass line 7 is provided in the area of the outlet side of the working medium pump 1, which opens at one end in the condenser 4 and thus mixes liquid working medium with the vaporized working medium flowing from the expander 3 into the condenser 4. The bypass line 7 comprises a valve 6, which can be implemented as a controlled overflow valve or pressure limiting valve, for example. It can also be a proportional valve which is actuated electrically, electromagnetically, pneumatically, or mechanically in this case. The valve 6 can be actuated by a central control unit, such as an onboard computer, for example.

Suitable sensors for recording the pressure can also be situated in the valve 6 and/or in the bypass line 7, which transmit signals for the regulation or control to a central control unit.

FIG. 2 shows a further exemplary embodiment of a steam circuit process device according to the invention, the same reference numerals as in FIG. 1 being used for corresponding components. For the illustrated exemplary embodiment, the bypass line 7 opens into a line 8 which connects expander 3 and condenser 4 to one another to conduct working medium. In the present case, the bypass line 7 therefore opens directly into the line 8 leading out of the expander 3, where the liquid phase from the bypass line 7 is mixed with the essentially vaporized phase of the working medium (exhaust steam from the expander 3). The connection point can be implemented as a T-shaped connection pipe, for example. A nozzle, which atomizes the liquid working medium from the bypass line 7, can be provided in the part of the connection pipe facing toward the bypass line 7. The nozzle can also be situated in the bypass line 7. An enlargement of the liquid surface of the liquid working medium is to be performed by the nozzle, so that the vaporized working medium leaving the expander 3 cools off more rapidly when it hits the liquid droplets of the atomized working medium. Atomization can be performed, for example, by suction or supply of air, such as ambient air. Of course, it is also conceivable to apply the liquid working medium from the bypass line 7 in the connection pipe and/or in the supply line by wetting on the inner sides of the line 8 or the connection pipe.

Furthermore, manifold embodiments are conceivable, the basic principle remaining the same: The working medium is branched off at the exit of the working medium pump 1 or downstream from the working medium pump 1, before or in the area of the vaporizer 2, and supplied to the vaporized working medium of the expander 3 for cooling.

LIST OF REFERENCE NUMERALS

-   1 working medium pump -   2 vaporizer -   3 expander -   4 condenser -   5 reservoir -   6 valve -   7 bypass line -   8 line 

1-13. (canceled)
 14. A steam circuit process device, comprising: a reservoir for a liquid working medium; a vaporizer, in which the working medium is vaporized by supplying heat, the vaporized working medium being supplied to an expander to expand and perform mechanical work and subsequently being liquefied in a condenser, which is connected to the reservoir; a working medium pump for supplying working medium from the reservoir to the vaporizer; characterized in that liquid working medium is supplied to the working medium exiting from the expander before or in the area of the condenser in the working medium flow direction.
 15. The steam circuit process device according to claim 14, characterized in that a bypass line is provided for the supply of the liquid working medium, which produces a connection between the output side of the working medium pump and the intake side of the condenser.
 16. The steam circuit process device according to claim 15, characterized in that one end of the bypass line opens into a line between expander and condenser.
 17. The steam circuit process device according to claim 15, characterized in that one end of the bypass line opens into the condenser.
 18. The steam circuit process device according to claim 15, characterized in that one end of the bypass line opens into the expander.
 19. The steam circuit process device according to claim 15, characterized in that a valve is situated in the bypass line, using which, by changing the working medium volume flow through the bypass line, the pressure and/or volume flow of the working medium, which is not branched off through the bypass line, to the vaporizer can be regulated or controlled.
 20. The steam circuit process device according to claim 19, characterized in that a regulating/control unit is provided, using which the opening cross-section of the valve is adjustable in such a manner that the volume flow curve and/or the pressure curve in the supply line to the vaporizer follows a predetermined target curve, which results from the power demand at the expander.
 21. The steam circuit process device according to claim 19, characterized in that at least one pressure, volume, mass flow, and/or temperature sensor is provided, which records the corresponding variable of the working medium leaving the vaporizer and transmits it via at least one line to the regulating/control unit, so that the volume flow curve and/or the pressure curve in the supply line to the vaporizer is adjustable as a function of the temperature of the working medium leaving the vaporizer.
 22. The steam circuit process device according to claim 20, characterized in that at least one pressure, volume, mass flow, and/or temperature sensor is provided, which records the corresponding variable of the working medium leaving the vaporizer and transmits it via at least one line to the regulating/control unit, so that the volume flow curve and/or the pressure curve in the supply line to the vaporizer is adjustable as a function of the temperature of the working medium leaving the vaporizer.
 23. A method for controlling a steam circuit process device according to claim 14, characterized in that the working medium volume flow delivered by the working medium pump varies independently of a target value for the pressure and/or the volume flow of the working medium to the vaporizer, and the working medium volume flow supplied to the vaporizer and/or expander is regulated and/or controlled in that a part of the working medium volume flow from the working medium pump is supplied to the working medium exiting from the expander.
 24. The method according to claim 20, characterized in that the liquid working medium as atomized before or during the supply to the working medium exiting from the expander.
 25. The method according to claim 20, characterized in that, at the point of the combination of liquid working medium and working medium leaving the expander, the inner side of the line, which guides the working medium from the expander, is wetted using liquid working medium.
 26. The method according to claim 23, characterized in that the amount of the part of the working medium volume flow from the working medium pump which is supplied to the working medium exiting from the expander is adjusted as a function of the temperature of the working medium exiting from the vaporizer.
 27. The method according to claim 24, characterized in that the amount of the part of the working medium volume flow from the working medium pump which is supplied to the working medium exiting from the expander is adjusted as a function of the temperature of the working medium exiting from the vaporizer.
 28. The method according to claim 25, characterized in that the amount of the part of the working medium volume flow from the working medium pump which is supplied to the working medium exiting from the expander is adjusted as a function of the temperature of the working medium exiting from the vaporizer.
 29. A drive unit for a vehicle, comprising: a steam circuit process device according to claim 14; an internal combustion engine whose exhaust gases are supplied to the vaporizer for heating and/or vaporizing the working medium; characterized in that the internal combustion engine at least indirectly drives the working medium pump.
 30. A drive unit for a vehicle, comprising: a steam circuit process device according to claim 15; an internal combustion engine whose exhaust gases are supplied to the vaporizer for heating and/or vaporizing the working medium; characterized in that the internal combustion engine at least indirectly drives the working medium pump.
 31. A drive unit for a vehicle, comprising: a steam circuit process device according to claim 16; an internal combustion engine whose exhaust gases are supplied to the vaporizer for heating and/or vaporizing the working medium; characterized in that the internal combustion engine at least indirectly drives the working medium pump.
 32. A drive unit for a vehicle, comprising: a steam circuit process device according to claim 17; an internal combustion engine whose exhaust gases are supplied to the vaporizer for heating and/or vaporizing the working medium; characterized in that the internal combustion engine at least indirectly drives the working medium pump.
 33. A drive unit for a vehicle, comprising: a steam circuit process device according to claim 18; an internal combustion engine whose exhaust gases are supplied to the vaporizer for heating and/or vaporizing the working medium; characterized in that the internal combustion engine at least indirectly drives the working medium pump. 